It is conjectured that he is the patron of Beltane (the First of May), and the god refered to by Julius Caesar as Apollo. The identification with Beltane is likely based on two texts: Cormac's Glossary, which says that Beltane is named for Bel, and that cattle were driven through two bonfires to purify them; the same idea is echoed in Tochmarch Emire:

To Beldine, i.e. Beltine, viz., a favouring fire. For the druids used to make two fires with great incantations, and to drive the cattle between them against the plagues, every year. Or to Beldin, viz., Bel the name of an idol. At that time the young of every neat were placed in the possession of Bel. Beldine, then Beltine.

If there is any possible basis for this idea, it is perhaps that Belenos, like Apollo, may have had some special association not only with the sun or fire, but with cattle as well. Of course, it could also be that these two Irish texts were extrapolating from Belenos' name bel-, refering to shining.

Elsewhere, Belenos is also possibly associated with prophecy. If the editors of the Celtic Culture encyclopedia are correct, his name may be derived from belisa, the word for henbane, a psychoactive drug. This would strengthen his tie to Apollo, who has his own famous oracle at Delphi.

His name may be related to the god Mars Belatucadros, or "Mars the Shining One". While Belenus is referred to as Apollo and Belatucadros as Mars, the interpretatio romana should not be a stumbling block when one sees the similarities.

Sites of Worship
The healing wells at Sainte-Sabine, Burgundy, were dedicated to Apollo Belenus. Other inscriptions to Belenos have been found in Aquileia (CIL V 732-755), Provence, Nîmes (where he is carved onto a jewel (CIL XII 5693,12), and depicted as an older man in a tunic (CIL XII 5958), Iulium Carnicum (CIL V 1829), Concordia (CIL V 1866), Altinum (CIL V 2143-2146), Rome (CIL VI 2800), and Rimini (CIL XI 353). There are also a few Gaulish inscriptions, such as at Saint-Chamas (RIG I G-28), Marseille (RIG 1 *G-24 partially destroyed) and Satin-Remy-de-Provence (RIG I G-63),

CIL V 732-755, and 8212 all refer to Belenus, either simply as Belenus, or with Apollo or Augustus attached.

Classical references
Belenos is one of those rare Celtic gods who made an impression not only in Roman consciousness, but in Christian, too, for he is mentioned by Tertullian as being worshipped by the Norici tribe, at that time part of the Noricum province, now Austria.

Ausonius, a Gallo-Roman poet of the late fourth century, speaks not only of the druids of Bordeaux, but of one Phoebicius, priest of the temple of Belenus.

Another tie to Apollo is found in the history of Herodian: his reported appearance above a battlefield in Aquileia, Italy. The emperor Maximinus besieged the city in 238; according to Herodianos, oracles testified that the city would be protected by Belenos, who was later attested to have been seen hovering over the soldiers, not unlike the Angel of Mons in WWI. The city did withstand the siege, outlasting the emperor, who was assassinated within four months.

Medieval Survival
Later legend makes him king of Britain, in the form of Beli Mawr (Beli the Great). See the entry on Beli Mawr for the complications on this identification.

Elsewhere, (namely in The History of the Kings of Britain), Belinus is made the brother of Brennius (Bran), and his rival. This rivalry may be a half-rememberence of the battles between the Children of Don and the Children of Llyr, as Bran was the son of Llyr, and Beli the consort of Don.

Geographically speaking, Belenus lives on; he gave his name to Beligna, Italy, while Bérenton, Brittany may be connected to him also.